Phosphorylated sulfonium salts have been prepared as the key high energy phosphorylating intermediate in respiratory chain linked oxidative phosphorylation. The mechanism by which such species might arise under biological conditions is under investigation. One suggestion is that electron deficient sulfides (cation radicals, dications, or their functional equivalents) are formed by one or two successive one electron oxidations. These intermediates then react with orthophosphate anion to form phosphorylated sulfonium salts. This suggestion requires that aliphatic sulfides be capable of oxidation under biological conditions and that the products so formed can, in the presence of orthophosphate anion, effect phosphorylation of ADP. Whether alkyl sulfides in biological systems can meet these requirements are under investigation. Other mechanisms for oxidative phosphorylation involving chemical intermediates are also under study.